3 sentences

1. 污染源主要来自这条河流的上游。

   wū​rǎn​yuán zhǔ​yào lái​zì zhè tiáo hé​liú de shàng​yóu.

   The source of pollution mainly comes from the upstream section of this river.

   Source: Dong Chinese Dictionary

2. 每年秋天，成群的鲑鱼都会游回上游产卵。

   měi nián qiū​tiān, chéng​qún de guī​yú dōu huì yóu​huí shàng​yóu chǎn​luǎn.

   Every autumn, schools of salmon swim back upstream to spawn.

   Source: Dong Chinese Dictionary

3. 船只在江面上逆着强风，缓缓地向上游前行。

   chuán​zhī zài jiāng​miàn shàng nì zhe qiáng​fēng, huǎn​huǎn de xiàng shàng​yóu qián​xíng.

   The boat moved slowly upstream against a strong wind.

   Source: Dong Chinese Dictionary